1. Field of the Invention
The present invention relates to an image input apparatus and system which sense an object image by dividing it into a plurality of photoelectric conversion areas.
2. Related Background Art
X-ray photography for medical diagnostic purposes is often performed by using a film screen system that uses a combination of sensitized paper and an X-ray photographic film.
According to this method, X-rays passing through an object contains information inside the object body, and the information is converted into visible light proportional to the intensity of the X-rays by the sensitized paper. As a consequence, the X-ray film is exposed to the visible light.
Recently, an X-ray digital image sensing apparatus has been used, which converts X-rays into visible light proportional to the intensity of the X-rays by using phosphors, converts the light into an electrical signal by using photoelectric conversion devices including a photoelectric conversion area that is formed by a single semiconductor substrate, and converts the signal into a digital signal through an A/D converter.
For example, the following X-ray digital image sensing apparatuses have been proposed: an apparatus in which phosphors for converting X-rays into visible light are stacked on a matrix of photoelectric conversion devices, each having electrodes sandwiching an amorphous semiconductor element, on a glass substrate; and an apparatus comprised of a two-dimensional array of modules each formed by arranging photoelectric conversion devices such as CCDs on the tapered side of a tapered optical fiber bundle softened and extended by heat and stacking a phosphor on the opposite side of the fiber bundle to the photoelectric conversion devices.
The above X-ray digital image sensing apparatuses are mainly used for medical diagnosis and the like. For early detection of abnormal portions and accurate diagnosis, there have been increasing demands for high resolution, low noise, moving images, wide image sensing areas, and the like.
The following problems are, however, posed in the above conventional X-ray digital image sensing apparatuses.
According to the apparatus using the photoelectric conversion devices formed from the semiconductor elements made of amorphous silicon or the like on the glass substrate, although a large sensor effective size can be attained, a reduction in pixel size is difficult to achieve in terms of process and device characteristics.
According to the apparatus using the photoelectric conversion devices such as CCDs formed on the silicon substrate, a reduction in pixel size can be achieved, and moving images can be obtained because the apparatus has high sensitivity and can be driven at high speed. However, a large sensor effective area cannot be set owing to process limitations.
Under the circumstances, there is proposed an apparatus designed to increase the sensor effective area by increasing the number of photoelectric conversion devices using optical fibers tapered to prevent the non-sensor areas of the elements from overlapping, as shown in FIG. 1. Referring to FIG. 1, this apparatus is comprised of photoelectric conversion devices 1 including photoelectric conversion areas, a scintillator 2 for converting X-rays into light such as visible light having a wavelength that can be detected in the photoelectric conversion areas, tapered optical fibers 8, protective glass plates 10, bonding wires 11, and ceramic packages 12. However, these tapered optical fibers are expensive, thick, and heavy. This makes it impractical to obtain a sensor effective area required for chest photography, even though several such optical fibers can be coupled to each other.
Owing to these problems, it is difficult to satisfy all the requirements for an X-ray digital image sensing apparatus for medical diagnosis, namely performance associated with high resolution and moving images, wide sensor effective area, and reductions in the size and cost of the apparatus.